WAREHAM — There was no reason Monica DeMello and Kathleen Allen should have met. But when they did, in the dark of night this weekend on a lonely stretch of two-lane highway, it was fatal.

Both were young and from Middleborough, but the similarities end there. DeMello, an 18-year-old Gordon College freshman home for Easter, was deeply religious and had a keen sense that her life would involve helping others. She didn’t smoke or drink alcohol.

Allen did both. At 23, she already had a string of open court cases suggesting a troubled life: charges of assault and battery with a dangerous weapon, drug possession, larceny. On Friday night, prosecutors say, Allen injected heroin, drank alcohol for hours and, sometime before 2 in the morning, climbed behind the wheel of a Dodge pickup.

She would tell police that as she drove on Route 44 in Lakeville, she dropped a cigarette and bent down to hunt for it. She swerved into oncoming traffic — wrestling briefly with a passenger who grabbed the wheel — and plowed head-on into DeMello’s Hyundai Accent.

Taunton Funeral Home

Monica DeMello, 18

DeMello suffered massive head trauma and was declared dead at the scene. The passenger in the truck, Megan Felton, was seriously injured and flown to Brigham and Women’s Medical Center in Boston. Allen sustained bruises from her seat-belt strap.

Her blood alcohol level, law enforcement officials said, was .14, almost twice the legal limit of .08.

At an arraignment in Wareham District Court on Monday morning, Allen was charged with motor vehicle homicide, drunken driving, and other traffic offenses, and was ordered held on $100,000 cash bail. Allen’s bail was also revoked on the unresolved cases.

“Her detention is necessary to reasonably assure safety to the community,” Mary Nguyen, a Plymouth assistant district attorney, said during Allen’s arraignment.

“The open cases involve violence, they involve drug use, they involve stealing from other people and, most importantly, she was on the roadway intoxicated, resulting in the death of an 18-year-old girl home for Easter,” Nguyen told judge Gregory Williams.

Patrick O’Leary, Allen’s attorney, pleaded not guilty on his client’s behalf. Allen, dressed in a grey sweater, stood in a holding area next to O’Leary and turned her back toward the courtroom in an effort to hide from cameras.

George Rizer for the Boston Globe

Relatives and friends of Monica DeMello, an 18-year-old Gordon College freshman home for Easter who was killed in a crash on Route 44 in Lakeville, observed proceedings in Wareham District Court on Monday.

The defendant’s mother attended the arraignment and afterward left the courtroom, sobbing as she walked to her car and sat in the front passenger’s seat, holding her hand over her mouth as an unidentified driver drove the car from the parking lot.

DeMello’s mother, Ana Smith, and stepfather, Matthew Smith, attended the arraignment. Anna Smith gasped and tears ran down her cheeks as Nguyen read from a police report about Allen’s alleged drinking and drug use in the hours prior to the crash.

Shocked family and friends mourned and on Monday visited a memorial near the scene of the accident.

“She was so beautiful inside and out,” said Cheri DeMello, Monica’s aunt. “She shined and she loved her family. She never cried, never complained, and always smiled.”

Allen told authorities she injected heroin into her arm and drank from 4 to 6 p.m. Friday, prosecutors said. Police were called to Allen’s residence at 35 Cambridge St. at 10:30 p.m. Friday by a neighbor complaining that she was drunk and disruptive. Police again crossed paths with Allen at 12:24 a.m. on Saturday, when they observed her appearing to be intoxicated and disruptive as she stood along Route 28 near West Street with her boyfriend, Nguyen said.

Allen was not taken into custody on either of those two incidents. Police said that on the first call, she disappeared by slipping out a back door at her apartment. In the second encounter on Route 28, police allowed her to leave and she jumped in the back seat of a friend’s pickup truck.

According to a police report, Allen told authorities that she took her eyes from the road when she dropped the cigarette and that when she realized she was in the opposite lane, she attempted to steer the truck left into a parking lot. But at the same time Felton, the passenger, grabbed the wheel and tried to pull right. The truck then hit the Hyundai driven by DeMello.

DeMello graduated last year from Bristol-Plymouth Regional Technical School in Taunton and was a freshman at Gordon College in Wenham, where she worked at the dining hall.

George Rizer for the Boston Globe

Mourners set up a memorial at the scene of the fatal accident.

Her family spent Easter making funeral arrangements. The wake will be Wednesday, followed by a private family funeral on Thursday at the Taunton Funeral Home.

Gordon College’s president, D. Michael Lindsay, issued a statement.

“This is a tragedy and a shock to all of us, especially on the eve of Easter,’’ he said.

Ryan Benharris, an attorney from Fall River who is a friend of DeMello’s family, served as a spokesman Monday morning, saying DeMello, who was majoring in psychology, was deeply religious and devoted to helping others.

“They [the victim’s family] will repeatedly tell you that she was not somebody that cared about herself; she cared about everybody else,” Benharris said.

“It’s a very, very difficult time for the family. At this time they’re very distraught. Mr. Smith, he’s a firefighter, he’s seen a lot of accidents, a lot of things like this but when it’s your own family, it’s something that you can’t even comprehend.”

Alisha Packe, who was at the Wareham District Court on an unrelated personal matter, said she grew up in the area and that drunken driving has claimed the lives of six of her friends since high school.

“I feel terrible for Monica’s family; people really need to be careful and stop drinking and driving, because it’s nothing to mess around with,” Packe said.